Crystal structure prediction via evolutionary algorithm

Who (supervisor): Niloofar Zarifi (John Tse)
Venue: PEGASUS Student Summer Seminar, Aug 23, 2012.
 Abstract: The ability to predict the structure of a solid presents a challenge to the chemistry, physics, and material science communities. The difficulty of crystal prediction comes from the complexity of the potential energy landscape of a solid, which depends on many variables like unit cell parameters. Moreover, it may not be known how many atoms comprise the primitive unit cell. Particle swarm optimization and genetic algorithm are two powerful techniques to structure determination. These two methods are extremely successful to predict stable or metastable structures at given extreme condition.

Computational Studies on Alternative Materials for Lithium-Ion Batteries

Who (supervisor): Jianjun Yang (John Tse)
Venue: PEGASUS Student Summer Seminar, Aug 16, 2012.
Abstract: Lithium ion batteries are widely used in portable electronics because of their high energy density and low weight, and they are currently intensively investigated for more demanding applications such as electrical vehicles and for the stationary power backup systems. To improve its performance, computational modeling has become an essential component in design of new battery materials in addition to the physical work in laboratories. This talk will outline the major challenges of the current Li-ion batteries and summarize several successful computations on the alternative materials.  My own research work on the Li-ion battery materials will be introduced at the end.

Coupling the Higgs Boson to the Nucleon

Who (supervisor): Fred Sage (Rainer Dick)
Venue: PEGASUS Student Summer Seminar, Aug 9, 2012.
Abstract: The talk will explore possible methods of computing an effective Higgs-nucleon coupling. While the interaction of the Higgs with fundamental particles in the Standard Model of particle physics is well understood, how it couples to composite particles like the nucleon is less well understood. The physics of the Higgs boson itself will be reviewed, and then previous attempts at finding such a coupling will be discussed. Finally, several potential new methods will be given brief descriptions.


F-region plasma structures in the polar cap

Who (supervisor): Gareth Perry (J.P. St. Maurice)
Venue: PEGASUS Student Summer Seminar, July 12, 2012.

The spatial and temporal evolution of an F-region plasma patch, detected over Resolute Bay, has been studied with a suite of instruments. For this case study, the Resolute Incoherent Scatter Radar – North (RISR-N) is used to construct a three-dimensional image of the plasma parameters of the patch. Three Super Dual Auroral Radar Network (SuperDARN) systems along with optical imagers at Resolute Bay and Qaanaaq, Greenland are used to provide a multi-instrument overview of the both the patch and the high latitude F region during the event. SuperDARN was used to track the patch for nearly an hour, from the cusp region to Resolute Bay. During a 10 minute period, the patch was detected and identified in the RISR-N, Optical Mesosphere Thermosphere Imagers (OMTI) and SuperDARN instruments, yielding a unique opportunity to study the patch with multiple instruments. Of the more interesting findings of this study, one indicates significant density fluctuations within the patch, without any clear evidence for an external driver such as precipitation. The techniques and results of this case study will be described in this presentation, along with the insight which they provide to patch research. Also, a brief introduction to space physics will be given.

New Age Solar Cells: Dye-Sensitized and Nanocrystal Approaches

Who (supervisor): Paul Bazylewski (Gap Soo Chang)
Venue: PEGASUS Student Summer Seminar, July 5, 2012.
Abstract: Recently, organic semiconductor materials have received significant attention as potential solar cell materials. This is due to appealing properties that cannot be achieved with conventional inorganic semiconductors (silicon), such as low-cost solution based fabrication of large-area, mechanically flexible devices. Solution processing is low temperature and therefore ideal for flexible plastic substrates which cannot withstand the high temperatures required for inorganic processing. To date, significant progress has been made in polymer/small molecule bulk heterojunction (BHJ) organic photovoltaic (OPV) devices, achieving power conversion efficiencies (PCE) up to 8%. Although promising, this PCE falls below the benchmark for commercialization of ~10%. Therefore research has branched off to explore different device architectures and new materials, with the most successful approaches to date being dye-sensitized solar cells (DSSC) and hybrid nanocrystal-organic solar cells (HSC). These devices take advantage of organic dyes and unique properties of nanocystals such quantum confinement to improve PCE. This talk will outline the state of the art of these two new approaches, and introduce the research collaboration I am currently undertaking to develop high efficiency solar cell devices.

Plasma Ion Implantation for materials engineering

Who (supervisor): Sarah Purdy (Michael Bradley)
Venue: PEGASUS Student Summer Seminar, June 21, 2012.

Plasma Ion Implantation is a materials processing technique that can be used to modify the surface and subsurface structure of a material. A voltage bias applied to a conductive target immersed in plasma introduces a buried layer of impurities in the existing material. This processing technique has been applied to the modification of Si to produce silicon-based light emitting diodes (LEDs) with some success. Bulk silicon is not a light emitter due to its indirect band gap, but any photonic integration for multicore processing needs to be silicon based in order to be scalable for mass production. The work presented here is based on introducing carbon to a silicon wafer to introduce a buried layer of SiC – a known blue light emitter. With the introduction of a buried layer with significantly different stoichiometry from the native material, we see the appearance of delaminated blister features in the layer.

Band gap investigation of photocatalytic energy materials

Who (supervisor): Eamon McDermott (Alex Moewes)
Venue: PEGASUS Student Summer Seminar, June 14, 2012.
 Abstract: Eamon will give a brief overview of his research into the near-band gap electronic structure of energy materials, including semiconductor photocatalysts and lithium organics for use in alloying battery electrodes

Click here for a PDF version of Eamon’s talk

[EXTERNAL] Calcination induced phase transformation of TiO2 hierarchical nanotube membranes: morphology, electronic structure, and luminescence

Who (supervisor): Lijia Liu (T.K. Sham, UWO)
Venue: PEGASUS Student Summer Seminar, June 7, 2012.

Hierarchical TiO2 nanotube membranes were synthesized from Ti metal foil using electrochemical anodization. The membranes were composed of densely packed TiO2 nanotubes and a layer of ultra-small secondary TiO2 nanotubes on the surface. Regular TiO2 nanotubes prepared using the similar method were used for comparison. Calcination was conducted to convert the as-prepared amorphous nanotubes to anatase and rutile.The electronic structures of these hierarchical TiO2 membranes were examined using X-ray absorption near-edge structures (XANES). It was found that upon the formation of the ultra-small surface nanotube layers, the membranes exhibit unusual luminescence properties; i.e. that the hierarchical TiO2 membranes of amorphous and anatase phase are found to emit near ultraviolet luminescence at energy higher than the band gap of anatase, and the emission band shifts to the energy of rutile band gap after the membrane were transformed to rutile phase. Such unique optical behavior of hierarchical TiO2 membrane was analyzed using X-ray excited optical luminescence (XEOL) in combination with XANES to reveal the correlations between luminescence and electronic structure of these materials.

Remote Sensing of Stratospheric Aerosol

Who (supervisor): Landon Reiger (Adam Bourassa)
Venue: PEGASUS Student Summer Seminar, May 31, 2012.

Limb scattered sunlight measurements made by the Optical Spectrograph and InfraRed Imaging System (OSIRIS) onboard the Odin satellite are used to retrieve vertical profiles of ozone, NO2 and aerosol extinction. The retrievals are performed through forward modelling of the atmosphere using SASKTRAN, a fully spherical, successive orders radiative transfer model developed at the University of Saskatchewan. The current aerosol extinction data product is retrieved using an assumed lognormal particle size distribution for typical background conditions. This assumption can produce a systematic error in the result for cases where the size distribution is affected by volcanic aerosol. This work explores the feasibility of retrieving particle size distribution parameters directly from the measurements. Explored here is the possibility of using both multi-spectral extinction and coincident measurements at different scattering angles, obtained on the ascending and descending portions of the orbit, to retrieve particle size information. These results will be used to improve the current aerosol extinction retrieval.

New model for polychlorinated biphenyls (PCBs)

Who (supervisor): Jay Forrest (Gap Soo Chang)
Venue:  PEGASUS Student Summer Seminar, May 17, 2012.
Abstract: Here we present a new model for the toxicity of polychlorinated biphenyls (PCB).  This model works on a first-principles basis, where it takes into account the basic electronic and electron transfer characteristics of the PCBs, investigated using Density Functional Theory.  The model shows bandgap as the overarching indicator of toxicity, but not the only factor.  Our model explains the why both para- positions are required for high levels of toxicity.  To rank the PCBs on a one-by-one basis, the dipole moment in relation to the most chemically active Cl-sites is critical.  The theory is consistent with accepted the Toxic Equivalency Factor (TEF) model for these molecules, and is also able to improve on it to rank the toxicity of PCBs of similar TEF.  This new model also includes a 13th dioxin-like PCB not under the TEF model, PCB 74.  The model is applied to bandgap measurements of a set of PCBs and the measurements are consistent with the model.  Bandgap measurements also indicate the bio-accumulative nature of PCBs.